The technical field of the invention is laser systems and, more particularly, the conservation of excitation media in gas lasers.
Gas lasers typically rely upon a pressurized gas which is excited to a light-emitting state by a high voltage electrical pulse. The chamber of a gas laser is usually constructed such that a small volume of the working gas medium is confined in a discharge zone between two electrodes. A small portion of the gas in the chamber is consumed in the electrical process of generating each laser pulse. A circulatory system (e.g., a fan or blower) continually recycles fresh gas into the discharge zone.
The gas in such a system undergoes a slow process of degradation, and eventually the energy produced by the laser pulses decreases. When the performance of the laser decreases below a threshold output energy level or the beam profile is degraded or shot-to-shot energy variations are observed, the gas in the chamber must be replaced with new gas.
The length of time a laser can operate without requiring the gas in the chamber to be replaced is called the gas lifetime. This length of time is a critical factor in the operation and value of gas lasers.
The present invention is directed toward fabricating excitation chambers which provide longer gas lifetimes than those of present laser systems.
The gas lifetime is related to the materials within the chamber which come in contact with the gas. The type of materials that form the structural elements of the chamber have a significant impact on the gas lifetime. The excitation chambers and the elements within it can be constructed out of various materials, such as metals, ceramics and plastics.
Most metals have little effect on the degradation of a gas in a chamber. However, metal components are typically expensive and are ill-suited for those elements of the chamber which come in close contact with the discharge zone because they can induce electrical arcing.
Ceramic materials, likewise, have little effect on the working medium, and because of their dielectric properties, can be used without risk of electrical discharges. However, ceramic materials are also expensive and difficult to fabricate in complex shapes. Moreover, because of their brittle nature, they are unsuitable for moving parts (such as blowers) or for parts that experience mechanical stresses.
Plastics also present problems in use. Several types of plastics are commonly used in the construction of laser excitation chambers in lasers because they are inexpensive, durable and easily shaped into parts. However, plastics tend to release volatile organic compounds over time, particularly in the harsh environment of a gas laser head assembly This "outgassing" of organic molecules significantly contributes to a shorter gas lifetime.
The problem of organic molecule outgassing has been identified by others. See, for example, Tennant et al., "Long-Life, Maintenance-Free Excimer Lasers", Proceedings of the Conference on Laser Eng. and Optics, Abstract No. TUU1 (1988). In this presentation, the authors suggested that elimination of organic materials and careful selection of metals and seals can extend laser gas life. However, this approach would preclude the use of plastic components.
Accordingly, there exists a need for better materials for use in gas laser excitation chambers. Compositions which can be inexpensively and readily fabricated into laser head assembly elements and withstand the conditions experienced during laser operation without contributing to the degradation of the working gas medium would satisfy a long felt need in the art.